Electric alarm apparatus



Patente-d Mar, l?, l925.

LSAE@ PA'IN'I GFFEQE.

GEO'RG SCHMIDT, 0F REINICKENDORF-OST, AND CARL BKER, 0F BERLIN, GERMANY,ASSIGNORS TO BAYERISCHE VEREINSBANK, OF MUNICH, GERMANY.

ELECTRIC ALARM APPARATUS.

Application filed May 6,

To all whom t may concern:

Be it known that we, GEORG SCHMIDT and CARL Bxnn, both citizens of theGerman Republic, residing at the 1st, Reinickendorf- Ost, the 2nd,Berlin, Germany, have invented certain new and useful Improvements inElectric Alarm Apparatus, of which the following is a specification.

This invention relates to an alarm and signaling apparatus designed toprotect against burglary and lire. In an apparatus of this character, asis well known, two selenium cells or two similarly acting electric lightcells are employed in connection with a IVheatstone bridge. Devices ofthis construction have the selenium cell, together with the storagebattery and the relay employed in connection therewith usually connectedin series and upon the device operating the current resulting foroperating the device is of a low intensity. Furthermore, in the seleniumapparatus of this character the same will opera-te to give an alarm uponthe slightest increase of the surrounding temperature. The relayemployed must be very finely adjusted in order to signal a feeble gleamof light. The release of the alarm circuit is effected either byexposure or by shading, or by exposure and shading of one or severalselenium cells. According to this invention the arrangement has beenmade, that a working cell and a compensating cell are compensated by tworesistances in a Wheatstone bridge in such a manner that the relay inthe bridge is currentless. Thus it is ensured that the relay acts onlyupon the electric light current and that the signalling device signalseven a very feeble gleam of light. The inertia and the inconstancy ofthe working cells are overcome further by the connection which has beenjust described. The alarm may be given according to this invention by afeeble gleam of light.

In order that the invention may be clearly understood, we will hereafterdescribe the same with reference to the form of construction which isdiagrammatically shown by way of example in the accompanying drawing,wherein 71 and V2 are two selenium cells. W1 is enclosed in the case orbox H which excludes all light; W2 is situated behind an indicator diskdrop K which closes a win- 1921. Serial No. 467,277.

dow tightly and is adapted to be swung sidewards and away from thewindow by the action of magnet M1. VV and W4 are the compensatingresistances. In the Wheatstone bridge the relay R is arranged which isdesigned to close the alarm circuit by means of the hand Z and theadjustable contacts K1, K2. FS is a fuse for feeble currents and willfuse when the leads 2, 4 are bridged over, provoking thus the alarmsignal. The multiple point switch Sct serves to cut in the alarmapparatus. Ms is a maximum switch designed to short circuit the contactof the relay when the said relay has been operated, so that the relay isprotected against over loading. L is an optical signal and G is anacoustic signal. The battery B supplies the required energy.

The operation is as follows When tlie'wdevice has to be switched on, theroom to be protected haswto be darkened, whereupon the switch Sch isturned so that the switch lever P is in contact with II.

The circuit is now as follows From the positive pole of the batterythrough lead 3, switch lever P, contact II, lead 31, lead 4, screw D,spring F, armature A, wire C, winding of magnet M1, lead 2a and backthrough leads 2, l to the negat-ive pole of the-battery B. Owing to thiscircuit the armature A is attracted by the electromagnet M1 and the diskK drops away from the selenium cell W2. The spring F is thus moved awayfrom contact screw D so that the current supply to the winding of magnetM1 is interrupted. The switch Sch is now moved to its operative positionthat is to say the switch lever P is placed upon the contacts III, IV.

The closed circuit current flows as follows v From the positive pole ofthe battery B, through lead 3, switch lever P, contact III, lead 3b andis then divided, a part thereof flowing through fuse FS, lead 4,selenium cell W2 to selenium cell W1, lead 2, and the remainder throughlead 4, resistances W4, W3 and lead l back to the negative pole of thebattery B. In the bridge of these connections the relay R is insertedbetween the leads 5 and 511.

The open current circuit is as follows From the positive pole of batteryB through lead 3, switch lever P, contact IV,

lead 3, through bell G, lamp L,lead 1, through the winding of themaximum switch MS interposed in, lead 1 to the adjustable contacts K1,K2 and further from the negative pole of battery B over lead 1 to thecontact pointer Z.

The short-circuiting device X, Y of the maximum switch MS is connectedby the leads 1 and 1a with the contacts 731, k2 and by the leads la withlthe pointer Z. The plant is thus switched in ready for work. If*nowfamdlight ray penetrantgsgintomthe protected"roomsiivliwthe casewith the selenium vcellsv 71, W2 is situated, either from a lightedmatch, or from a lighted pocketlanter1`,'tli`e'"ie"si'stance'the'sfclenium cell"lvzdiases almostinstantaneously and the electric proportion which was established in theworking position is disturbed. Current will consequently flow throughthe bridge so that the hand of relay R comes in contact with k2 and thealarm device is operated. The current of the working circuitflows asfollows From the positive pole of battery B to 3, P, IV, 3c, G-L, 1, Ms,1, k2, Z, 1 to the negative pole of battery B. Owing to the closing ofthe circuit the armature Y of the maximum switch is attracted and comesin contact with screw X so that the contacts k2, cl, Z of the relay Rare bridged over by means of leads 1, 1a and the relay is released fromthe current. IVhen the closed current circuit is cut or when the leads 54, 5-2 are bridged over, the signal is given in the same manner. Whenthe leads 2--1 are directly short-circuited the alrm is operated by thefusing of the fuse F c When the apparatus is to be cut out the contactlever P is brought in contact with I so that the disk K is placed overthe selenium cell 72 by the action of the magnet M2.

The circuit is as follows:-

Positive pole of battery B, lead 3, P, I, 3a through the winding ofmagnet H2, lead 2, over leads 2, 1 back to the negative pole of B. Owingto the closing of this circuit the armature A is attracted by the magnetM2, the spring F is again brought in contact with screw B and the disk Kis placed in front of the selenium cell T2 so that this cell is shut oitlight-tightly. The switch Sch is now brought back to its initial Oposition. By this turning of the switch the apparatus is out out. Fireis signalled in the same manner.

7e claim 1. A device of the class described comprising a lVheatstonebridge, means for giving an alarm when said bridge becomes unbalanced, apair of selenium cells in differd ent legs of said bridge, whereby saidbridge will remain balanced under varying temperature conditions, and alight excluding enclosure for one of the cells.

2. In an apparatus of the character described, a lllheatstone bridge,means for giving an alarm when said bridge becomes unbalanced, lightresponsive resistances inserted in the legs of the bridge, proportionedto maintain the bridge balanced under varying temperature conditions andalso adapted to imbalance the bridge upon light falling upon either ofsaid resistances.

In testimony whereof we afliX our signatures in presence of twowitnesses.

GEORG SCHMIDT. CARL BKER. llitnesses OARL O. BKER, ELIZABETH VVALF.

